A model system for intestinal cancer has been developed which has been used for examination of problems involving pathogenesis, prophylaxis, and therapy of the disease. Lobund Sprague-Dawley (S-D) rats are inoculated by gavage with 1, 5, or 10 doses of 1,2 dimethylhydrazine (30 mg/Kg BW), or with Methylazoxymethanol acetate (MAM) at same dose level S.C. The autochthonous tumors resulting thereof can be reduced very significantly by administrations of low levels of indomethacin in the drinking water, initiated as long as 35 days after exposure to the carcinogen. Administrations of another prostaglandin blocking agent (aspirin) or of interferon I were not effective in preventing, nor in reversing the tumors. Differences in strain susceptibility to intestinal tumorogenesis induced by another chemical carcinogen (Methyl(acetoxymethyl) nitrosamine) (13mg/Kg BW IP): Lobund S-D rats are susceptible and Lobund Wistar rats are resistant to the development of tumors by this chemical agent.